This invention generally relates to material and/or load handling apparatus and more particularly to a positioning and off-loading apparatus as may be used in conjunction with high-lift cranes to carry, position, and off-load materials in ready access for personnel use.
For example, in the construction of a high-rise building it is conventional practice to use one or more of various type high-lift cranes in the building process to move heavy loads and/or bulky construction materials from the ground to various levels of the construction site. While these cranes are extremely useful in moving such loads vertically from the ground and/or horizontally where no obstructions exist, they are limited to the extent that such loads cannot be easily positioned within a confined or overcovered area. For example, a crane that is positioned above a high rise construction may easily lift many thousands of pounds of material vertically to any level of the construction. However, in order to off-load said materials at a specific level or floor, an extension of the floor outward1y of the building must be provided so that the load may be vertically lowered onto the floor extension, disconnected from the crane hooks, and thereafter moved into the building for use. Naturally, to provide such floor extensions at every floor level to off-load building materials is a dramatic waste of time, effort, and expense in the construction process. This is true even though the floor extension may be a portable unit since such units must be safety-secured to the building, must be sufficient to carry the heavy loads, and are not easily moved to various other areas of the same floor level.
To alleviate these and other problems I have developed apparatus to be used in conjunction with high-lift cranes that enable construction workers to off-load heavy and/or bulky loads of materials directly onto the floor level without resort to floor extenders or extensions. One such apparatus is a prior art device that I developed and which is illustrated in the drawings and will be described in detail hereinafter.
By way of example, FIG. 1 of the drawings is illustrative of my prior art apparatus generally indicated by reference numeral 10. The apparatus 10 comprises a main boom member 12 that carries one or more telescoping minor boom members 14a and 14b respectively within its framework and these may be extended or retracted in accordance with the type and weight of a load "L" to be carried by the apparatus 10. The main boom member 12 has two top-mounted eye flanges 16 that accept cable hookups from a crane hoist indicated generally at 18, which hoist carries the apparatus 10 aloft for delivery of a load "L" to various levels of the construction site. Positioned at the outer extent of one end 10a is a load hook 20 and it will be immediately recognized by those knowledgeable in the load handling arts that a load "L" positioned at 10a must be counterweighted at the opposite end 10b such that the boom apparatus 10 remains in a substantially horizontal attitude during the lifting operation. In this circumstance, I have mounted a counterweight 22 on the main boom member 12 that is automatically movable therealong such that various load weights at 10a may be correctly compensated. To accomplish movement of the counter-weight 22, I have provided an electric motor (not shown) within the confines of the main boom framework and the required battery power and drive mechanism such that an electric control 24 may be used to position the counterweight at the proper position along the boom 12 for load compensation. The control 24 has a "forward" button for moving the counterweight in one direction and a "reverse" button for moving the counterweight 22 in the opposite direction along the boom 12.
The counterweight 22 is a block of a heavy material such as lead of approximately 2,000 pounds and additional 1,000 pound blocks may be added to a capacity of about 4,000 pounds. At capacity, the apparatus 10 may lift loads "L" of about 12,000 pounds. It should now be appreciated that the above described apparatus 10 allows a conventional vertical lift crane to carry a material load "L" to a particular floor level of a construction site and off-load said material directly into a building and onto a floor level without resort to exterior floor extensions. While the booms 14a and/or 14b may be extended to increase the horizontal reach of the apparatus 10, the counterweight 22 is movable toward the load such that it lowers it to the floor for disconnection.
While the above-described prior art apparatus 10 works well in its intended application, it does suffer from various disadvantages. These disadvantages include (a) the overall weight of the apparatus due to the counterweight limits the load capacity to be carried, (b) the total amount of counterweight is limited by the structural limitations of the booms, (c) the movable distance of the counterweight to compensate the load "L" is limited, (d) the extensibility of the minor booms to move the load away from the center-of-lift of the main crane for off-load positioning is limited, (e) the required battery power and motor drive to move the heavy counterweight along the main beam for load compensation is limited by weight considerations, and (f) the fact that the load "l" is carried at one end of the apparatus while it is being positioned for off-loading in close spaces presents a hazard.
To this end, my present invention is a marked improvement over the prior art in that it completely eliminates the requirement for counterweighting a load. Additionally, the present invention eliminates telescoping booms and the manner of their mounting within the main boom member and each other but instead provides a much simpler and stronger beam construction that is capable of carrying extremely heavy loads. Further, the present invention more advantageously carries a load "L" at the center-of-gravity of the apparatus during the lifting operation. The load "L" is therefore carried axially through the center-of-lift of the main lifting crane hookup which inherently has a greater lifting capacity. Eliminating the the counterweight of the prior art apparatus has the added benefit of significantly reducing the weight of the apparatus, which weight may instead be transferred to actual load carrying capacity. In addition, carrying the load "L" at the center-of-gravity allows for more easily positioning of the forward off-loading end into confined spaces and enhances the overall safety of the apparatus.